In recent years, a nitrile hydratase, which is an enzyme having an activity of hydrating a nitrile group and converting it to an amide group, has been discovered. A method for producing from a nitrile compound, an amide compound corresponding thereto, using the above enzyme, the cell mass of microorganisms containing the above enzyme, or the like, has been disclosed. This production method has been known as a method, which brings on a higher conversion rate to convert a nitrile compound to an amide compound corresponding thereto and a higher selectivity than those of the conventional chemical synthesis method.
Examples of the microorganisms that produce a nitrile hydratase may include microorganisms belonging to genus Corynebacterium, genus Pseudomonas, genus Rhodococcus, genus Rhizobium, genus Klebsiella, genus Pseudonocardia, or the like. Of these, Rhodococcus rhodochrous J-1 strain has been used for the industrial production of acrylamide, and the usefulness thereof has been verified. In addition, a gene encoding a nitrile hydratase generated from the cell strain has also been discovered (refer to Reference 1). Moreover, from the viewpoint of reduction in the amount of enzyme used during the reaction and cost reduction, it has been desired that an enzyme having an improved heat resistance be obtained.
A nitrile hydratase isolated from microorganisms existing in nature or the gene thereof has been used. On the other hand, an attempt to introduce a mutation into a nitrile hydratase has been made for the purpose of altering the nitrile hydratase in terms of its activity, substrate specificity, Vmax, Km, heat stability, stability to substrate, stability to the product generated, etc. (refer to References 2 and 3).